I might be missing something, but I still don't see where anybody says the bullet diameter is .255" I see that the caliber designation is .255, but with the Brits of that era the caliber designation was normally the bore and not the grooves. Thus, I suspect this is closer to a 6.5mm or .264".

Correct me if I have overlooked the obvious. I don't claim any knowledge of this round and had never taken note of it before this post.

Curl